The kinetics of formation and structure of anodic oxide films on tantalum

Abstract

The rate of formation of anodic oxide films on tantalum was studied using aqueous electrolytes. The thicknesses of the oxide films were measured by comparing the interference colors with a calibrated step gage. The equation which describes the kinetics of formation of the films is dx dt = A exp (BF − Q kT ) where B ≠ ƒ(T). This equation is not in agreement with the predictions of a recent theory by Mott and Cabrera which should apply to this process. The rate of formation of a film is not affected by its past history, the state of cold work of the metal, or by changes in the nature and concentration of the aqueous electrolyte. The efficiency of the process is 98 per cent at all temperatures and rates of formation. The films consist of amorphous Ta 2O 5, and recrystallize between 500 and 800°C.